The invention relates generally to the control of rolling mills in a manner that offsets the cyclic effects of roll assemblies, hereinafter called eccentricity, on the thickness of material being rolled.
A system for controlling the effects of roll eccentricity in a rolling mill is disclosed in U.S. Pat. No. 4,222,254 to King et al, the disclosure of this patent being incorporated herein by reference. An improvement in the King et al system is disclosed in pending U.S. Ser. No. 591,277, filed Mar. 19, 1984 in the name of Mark Puda, now U.S. Pat. No. 4,531,392. The disclosure of the Puda patent is also incorporated herein by reference.
Both the King et al and Puda disclosures employ a process by which the eccentricity of one or more roll assemblies of a mill is inferred by making mathematical estimates of eccentricity. Such estimates of eccentricity are made because the actual eccentricity of the rolls is not readily observable.
The estimates made in the King et al patent and the Puda patent are based on measurements of changes in the force at which the rolls of the mill engage the material being rolled in the mill, measuring changes in the stretch or compression of the mill housing during the rolling process and measuring changes in the position of the actuator mechanisms (mechanical screws or hydraulic cylinders) that control the working space and rolling force of the mill. These measurements are then used in a gaugemeter equation to estimate changes in the thickness of the material exiting the mill due to roll eccentricity.
The estimating process is continuous until the cyclic component in exit thickness due to roll eccentricity is reduced to a minimum or zero amount and the estimate of eccentricity reaches a steady state value representing the true eccentricity of the rolls.
As discussed in the Puda patent, the load cells and actuator mechanisms of the mill do not respond as fast as the occurrence of the eccentricity disturbance at high travel speeds of the material through the mill. Hence, the resulting control signals of the system can contain a delay in their response to eccentricity. The Puda disclosure cares for this by a process of developing phase compensated gains that are used to modify the amplitude and phase of the estimate of eccentricity calculated by the means disclosed in the King et al patent. The control signals directed to the actuator mechanisms of the mill are thereby phase corrected to care for the delay in the response of the load cells and actuator mechanism.